Date: Thu, 13 Nov 2008 22:34:38 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-hackers@freebsd.org Cc: freebsd-questions@freebsd.org Subject: Re: 128 Bucket Failures? Message-ID: <gfi6hk$6u8$2@ger.gmane.org> In-Reply-To: <F349C4D5-EC11-4138-8D7F-17CD6C1A3C8B@hughes.net> References: <F349C4D5-EC11-4138-8D7F-17CD6C1A3C8B@hughes.net>
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Chris Pratt wrote:
> I have asked this before a couple of years ago but received no
> replies. I assumed that's because it's a somewhat obscure question.
> I'm still interested and thought I might try again in case someone
> new is watching this list who might know.
>
> A vmstat -z on my highest traffic server always shows the failures
> as below on 128 Bucket. It also goes to having 0 free rather soon
> after the system is restarted and never returns to having more than
> 1 free in that column and yet always has the highest number of
> requests by far. Does this mean anything significant? Is it
> something I should tune or even can be tuned?
UMA buckets seem to be some kind of cache for SMP-optimized allocations
- I hope someone who knows it better will explain them.
> Here is the output of the vmstat -z with everything chopped out
> besides the 128 Bucket line. The machine it's on is an 8 core 8 GB
> Tyan and shouldn't really be starved for anything in my way of thinking.
>
> vmstat -z
> ITEM SIZE LIMIT USED FREE REQUESTS FAILURES
>
> 128 Bucket: 1048, 0, 2043, 0, 13591, 6511069
What is the server used for?
Here's a snapshot from a very loaded apache+php+pgsql web server, uptime
60 days (since the last power outage):
16 Bucket: 76, 0, 42, 58, 125,
0
32 Bucket: 140, 0, 76, 64, 183,
0
64 Bucket: 268, 0, 74, 38, 438,
11
128 Bucket: 524, 0, 2060, 642, 788828,
6985
A generic advice would be to increase vm.kmem_size (you're using AMD64,
right?) and see what happens.
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